1. Field of the Invention
The present invention relates to a seal device which is fabricated to a special form from a sheet material. More particularly, this invention relates to a seal device which is installed in assembly components wherein a clearance between mount surfaces thereof varies due to fluid pressure, vibratory external force, thermal expansion or contraction or the like.
2. Description of the Related Art
In an apparatus in which a seal device is installed between mount surfaces of adjacent assembly components for a sealing purpose thereat, a gap between the mount surfaces is forced to vary because of external forces, which causes a problem of decreasing in seal ability of the seal device. As an example, a seal ring is widely known for a gas turbine engine. The seal ring is used in a gas or steam turbine engine in which the ring is installed between mount surfaces which are subjected to thermal expansion stress of high temperature combustion gas or deformation due to compressed air pressure or vibratory force during rotary movement (see U.S. Pat. No. 6,237,921.B1 for instance). Mount surfaces in a gas turbine, nuclear apparatus or the like are exposed to high temperature, high pressure environment, thus a dimensional change between the mount surfaces being likely to occur. There is another type of seal ring used for such applications (see U.S. Pat. No. 4,121,843 for instance).
FIG. 7 depicts a seal ring which is similar to the one disclosed in FIG. 1 of U.S. Pat. No. 6,237,921.B1. As shown in FIG. 7, the seal ring 120 has U-shaped cross-section thereof. Both end portions of the U-shaped seal ring 120 define reverse bend portions 132, 132. The seal ring 120 is a two-ply construction consisting of an inner ring 122 and an outer ring 126. Also an inner circumferential portion of the inner ring 122 defines a groove 135.
The seal ring 120 is used to effect a seal against a high pressure turbine nozzle 110 of a gas turbine. The high pressure turbine nozzle 110 retains a plurality of nozzle vanes 112. The nozzle bane 112 is mounted to a radially inner band 116 in an integral manner which is supported by a support flange 118. The seal ring 120 is arranged between the inner band 116 and the support flange 118 in order to bring the inner band 116 of the high pressure turbine nozzle 110 into sealing contact with the support flange 118.
In this high pressure turbine nozzle 110, high temperature combustion gases 114 received from an upstream combustion chamber (not shown) is turned and accelerated through the nozzle vanes 112. The inner band 116 and the support flange 118 start to receive thermal deformation as heating proceeds. The seal ring 120 which is disposed between the inner band 116 and the support flange 118 impaired by the deformation due to thermal expansion is forced to undergo elastic deformation to an axial direction. Under this circumstance, a contact point 125 of the seal ring 120 which is located at the center of a U-shaped bending portion is supported by the support flange 118. This causes the seal ring 120 to have the reverse bend portions 132, 132 brought into contact with the inner band 116 and the support flange 118 and axially extending slots 134, 135, 134 are formed at three locations from the illustrated left to right along the reverse bend portions 132, 132. Therefore, although the seal ring 120 exhibits a wide range of elastic deformation in the axial direction, it becomes increasingly more difficult for seal faces 132A, 132B of the seal ring 120 which are resiliently supported by the U-shaped resilient member at the contact point 125 to achieve a uniform contact force because of such large elastic deformation. That is, the seal faces 132A, 132B may fail to keep up with the movement of the inner band 116 and the support flange 118, which will cause decreasing in seal ability thereat.
Out of the three open-ended slots 134, 135, 134 of the seal ring 120 with U-shaped cross-section, the largest slot 135 formed in the inner circumferential side has its open-ended portion in an opposite direction to the other two small slots 134 which are relatively located to the both sides of the largest slot 135. Therefore, such a configuration increases the production cost because of the difficult bending process involved.
FIG. 8 shows a seal ring 216 with an “E”-shape cross-section. The seal ring 216 consists of a couple of U-shaped cross sectioned members, first annular seal portion 220A and second annular seal portion 220B, which are joined at one end by means of a middle bridge portion 225. A middle groove 210 is formed between the first annular seal portion 220A and the second annular seal portion 220B in the illustrated above of the middle bridge portion 225. A first elastic portion 224A and a second elastic portion 224B which are joined by the middle bridge portion 225 are continuously extended to form a third elastic portion 226A and a fourth elastic portion 226B of a semi-circular section, respectively. The semi-circular third elastic portion 226A and fourth elastic portion 226B, respectively, retain arcuate first seal face 222A and second seal face 222B at outer circumferential sides thereof which are brought into contact with assembly components. The seal ring 216 enjoys resiliently urging force according to a distance from the middle bridge portion 225 to the respective first seal face 222A and the second seal face 222B via first elastic portion 224A and second elastic portion 224B.
In the seal ring 216, because of the semi-circular form of the third elastic portion 226A and the fourth elastic portion 226B which are located at the opposite ends of the first elastic portion 224A and the second elastic portion 224B relative to the middle bridge portion 225, respectively, the first seal face 222A and the second seal face 222B may fail to maintain seal-tight contact against assembly components. That is, the elastic deformation forces of the first elastic portion 224A and the second elastic portion 224B rooted at the middle bridge portion 225 and evaluated at the first seal face 222A and the second seal face 222B are not significant enough to provide urging forces in such a way that the first seal face 222A and the second seal face 222B are always kept in uniform contact against the assembly components. This will lead to uneven and insufficient contact force of the first seal face 222A and the second seal face 222B, thus being likely to decrease in seal ability of the first seal face 222A and the second seal face 222B. The seal ring 216 also retains a third seal face 221A and a fourth seal face 221B via a fifth elastic portion 223A and a sixth elastic portion 223B, respectively, on the outer circumferential surface of the radially inward portion. The third seal face 221A and the fourth seal face 221B are said to be capable of maintaining seal-tight contact even in case of tilted mount surfaces of assembly components. As in the case of the third seal face 221A and the fourth seal face 221B, however, use of the middle bridge portion 225 as a fulcrum is likely to reduce the range of sufficient contact which the seal faces can achieve. Since the performance of the seal ring 216 needs to be evaluated as a total performance of the middle groove 210 and pressure receiving slots 134, 134 which are disposed sideways of the middle groove 210, it is not straightforward to manufacture precise dimension by a press forming process.
The present invention is introduced to resolve the above mentioned problems and the development of necessary technologies associated with the problems have been under way. A primary technical goal which this invention tries to achieve is to provide a seal device which is capable of exhibiting a substantial sealing ability over a wide range of dimensional change of a gap between seal mount surfaces which is caused by external forces due to a fluid pressure, heat-induced stress or the like. Another goal is to enhance seal structure thereof and reduce manufacture cost thereof. Yet another goal is to make the seal device compact such that it can be installed between narrow-gap mount surfaces and to reduce assembly cost. Yet another goal is to improve seal durability thereof.